A reported 3.7-magnitutde earthquake was actually an 'experimental explosion' caused by the U.S. Navy, according to the U.S. Geological Survey.

The explosion was reported just over 100 miles from Daytona Beach off the Florida coast at 4 p.m. Saturday. The Geological Survey reports that 68 people felt the force of the blast.

First Coast News has reached out to Naval Station Mayport but was referred to SURFLANT, the organization that oversees all surface ships off the coasts of the eastern United States.

Dale A. Eng, Public Affairs Specialist, for Naval Sea Systems Command told First Coast News the Navy began conducting Full Ship Shock Trials (FSST) for Littoral Combat Ship USS Jackson (LCS 6) off the coast of Florida.

He said the purpose of FSST is to validate the operational survivability of new construction ships after exposure to underwater shock. Three tests were scheduled for the ship and each test was conducted with a 10,000-pound explosive charge.

He also went on to say, "the Navy ensures an exclusion zone is established around the test location. A Notice to Mariners (NOTAM) is released before each shot stating that hazardous conditions to surface vessels may be present and for vessels not involved in the test to remain clear."

The Daytona Beach News-Journal reported a permit from the Fisheries Service for explosions conducted by the Navy was granted from 2013 to 2018 - that shock trials east of Jacksonville could include a 10,000-pound and a 40,000-pound charge.

The new littoral combat ship (LCS) Jackson was showered by spray and shaken by a large explosion June 10 as she endured the first of a series of controlled tests intended to prove the design’s ability to withstand combat and damage. Photo: U.S. Navy

On June 10, the littoral combat ship USS Jackson underwent a shock trial off the coast of Florida, Defense News reported. The Jackson is stationed at Mayport and is a new class of ship the Navy's commissioned, mainly to be used in surface combat situations.

In that trial, the Navy set off a 10,000-pound charge just a hundred yards from the ship. It survived.

The final test was scheduled for July 8, weather permitting.

This isn't the first earthquake that ended up being ruled as an experimental explosion - there was a 3.7 magnitude experimental explosion reported just under 100 miles off Flagler Beach on June 10.

This is a developing story. Stay with First Coast News for updates.